The present invention relates to an object detecting apparatus for detecting the presence of an object and determining if this object is on a collision course with a platform carrying the apparatus.
Object detecting systems are well-known in the literature. However, such systems have heretofore been applied to comparing an observed scene with either an earlier view of the scene retained in memory or a standard scene image retained in memory. Variations on such systems are used to guide missiles to infra-red "hot spots", often by proportional navigation based on line of sight change rates, and, in other variations, by a sequence of return signals reflected by the object from a sequence of signals transmitted by the system.
A surveillance system employing such an object detecting apparatus is described in U.S. Pat. No. 4,257,063 to Loughry, et al. In this apparatus, a television camera sans the desired scene in a known raster fashion in a series of image frames, producing an amplitude modulated video signal describing the energy intensity distribution of the scene. Clocking and gating circuitry triggered in synchronism with the television camera synchronization signals defines a set of predetermined discrete spaced locations of the raster during each image frame and samples the video signal amplitude at each of the defined locations. The same discrete locations are sampled during each frame. By appropriate storing the video amplitude signals, a profile of the amplitude distribution of the video samples taken during each frame may be produced. By comparing successive amplitude profiles at an appropriately determined and adjusted threshold, the appearance of an object into the scene may be detected.
A video inspection system, as described in U.S. Pat. No. 4,344,146 to Davis, Jr., et al, provides for digitizing the video signals produced by a television camera observing a scene and assigning a digital value to each "pixel" or elemental part of the overall picture. These values are then stored in a digital memory and are available for comparison processing by a digital computer either with a stored "standard" scene or with a subsequently digitized representation of the scene. Each pixel is compared with its corresponding time sequence of digital values.
An "active" object detection system is described in U.S. Pat. No. 4,512,000 to Masuko. A "passive" steering device system is described in U.S. Pat. No. 4,288,050 to Gauggel. U.S. Pat. No. 3,636,330 to Holeman, et al, describes a navigational system wherein a viewed scene is compared optically with a hologram produced to establish an inertial reference.
Recognizing the technology represented by the above-referenced sample of patents, the present invention is addressed to a simpler, yet possibly more complex problem. In maritime navigation and the operation of watercraft of all sorts, one of the principal concerns is that of collision with another craft. This is particularly true for the operation of small craft, normally in short waters. Among small craft, the problem is exceptionally serious for craft operating under sail, with their inherently reduced visibility caused by the disposition of the sails.
The usual criteria for determining if another craft is on a collision course with the craft on which an observer is stationed is to note the "angle on the bow" of the other craft at sequential increments of time. If the "angle on the bow" does not change over time, three conditions are possible. Either the two craft are diverging, they are on parallel courses at equal speed, or they are on a collision course. Only if the apparent size of the other craft is observed to increase over time does the collision course condition exist.
While the above illustration and the herein described preferred embodiment of the invention consider primarily the watercraft application, it is apparent that a similar approach can yield a collision avoidance alarm system for motor vehicles, and, if three dimensional space is considered, for aircraft. Such systems ar further capable of triggering evasive action through an autopilot.
The primary factors that impact upon the requirements for an effective collision avoidance alarm system for small craft are, without ordering their importance: low cost, wide-angle sensor to sense a closing craft against a changing background, an ability to sense a closing craft of a variety of size parameters which may vary as headings change, and other factors that may become evident through the subsequent descriptions. Each of these factors appear unique when the prior art is considered.